1. Field of the Invention
The present invention, relates to a method for the surface treatment of vacuum materials, and more particularly, it relates to a method for the surface treatment of vacuum materials which are used, for example, in vacuum apparatus for thin film deposition purposes in which semiconductors and electronic parts are produced.
2. Description of Related Art
In the past, it has been necessary with vacuum materials such as stainless steel which are used in vacuum apparatuses for thin film processing purposes, for example, to reduce the amount of gas which is released from the surface of the materials and to reduce the gas sticking probability of the surface. Water (H.sub.2 O) which is always present and which has a strong oxidizing action is especially important as such a gas. A surface treatment which can reduce the "amount of H.sub.2 O released" and reduce the "H.sub.2 O sticking probability" is very desirable. The "amount of H.sub.2 O released" signifies the amount of water which is released from the surface into the space when a vacuum material which has been present in an environment at atmospheric pressure is pumped out to a vacuum environment. On the other hand, the "H.sub.2 O sticking probability" signifies the proportion of the H.sub.2 O which does not rebound, but rather sticks to the surface of the vacuum material when H.sub.2 O is colliding with the surface of the vacuum material in the vacuum environment.
The units of the "H.sub.2 O sticking probability" reflect the number of H.sub.2 O molecules that will stick. For example, an "H.sub.2 O sticking probability" of 2.times.10.sup.-3 means that two H.sub.2 O molecules out of each one thousand molecules will stick.
Much research has been carried out into methods of surface treatment for reducing the "amount of H.sub.2 O released", and some of these methods have been put into practical use. These are generally methods in which the surface of the vacuum material is polished wherein an undesirable modified surface layer is removed either mechanically or chemically. Conversely, coating methods in which a film which has desirable properties is formed over the whole surface of the vacuum material are also in general use. Examples of such films include Cr.sub.2 O.sub.3 films (chromium oxide films) obtained by oxidizing the surface of the material itself, Si films (silicon films and silicon oxide films), and TiN films (titanium nitride films) which are obtained by deposition from the outside, and BN films (boron nitride films) which are obtained by diffusion from within the material. Cr.sub.2 O.sub.3 films have been disclosed in Japanese Unexamined Patent Applications (Kokai) H6-41629 and H6-116632, silicon oxide films have been disclosed in Japanese Unexamined Patent Application (Kokai) H4-337074 and BN films have been disclosed in Japanese Unexamined Patent Applications (Kokai) H7-62431 and H4-263011.
Conventional surface treatments, as described above, are all carried out to reduce the "amount of H.sub.2 O released", and their effect has been evaluated just on the basis of the extent of the "amount of H.sub.2 O released". The other factor, namely the "H.sub.2 O sticking probability", has not been evaluated at all. This is mainly because it is very difficult to measure precisely the "H.sub.2 O sticking probability", but it is also because it was thought generally that the two values were proportional, which is to say that the "H.sub.2 O sticking probability" should also fall as a result of a surface treatment which reduces the "amount of H.sub.2 O released".
An example of an investigation of surface treatment methods which measure the value of the "H.sub.2 O sticking probability" precisely is found in Japanese Unexamined Patent Application (Kokai) H9-91606. According to that application, the "H.sub.2 O sticking probability" is reduced by heating stainless steel in a specified atmosphere. However, care must be taken with handling the material after the treatment and, moreover, the values achieved are not satisfactory.